The present invention relates to improvements in processing textile strands, wherein variations in the strands caused by the manufacturing and handling of the strands are significantly reduced or eliminated, thus greatly improving the performance of the finished product incorporating the strands. In particular, this invention yields doubled yarn packages that are free of the vagaries normally found in such plied yarn and which are a result of the inconsistencies in strand manufacturing and the processing steps using the strands to make finished yarns. The improved processing involves the use of a heat treatment step and tension control to produce a doubled yarn package that is more uniform in physical characteristics than was previously possible using known techniques.
In the commercial manufacture of yarns, such as sewing thread, several strands of material are joined and processed to form the finished product. Strands are defined as an ordered assemblage of textile fibers having a high ratio of length to diameter and normally used as a unit. Strands can be composed of all natural materials, i.e. wool or cotton, or synthetics, i.e. polymers synthesized from chemical compounds (e.g. acrylic, nylon, polyester, polyethylene, etc.) or mixtures of the two. This invention involves the use of strands containing at least one synthetic material. Synthetic strands are manufactured using a spinning process wherein fiber-forming substances in the plastic or molten state, or in solution, are forced through the fine orifices in a metallic plate called a spinneret, or jet, at a controlled rate. The solidified filaments formed from the spinnerete are drawn-off by rotating rolls, or godets, and wound onto bobbins or pirns. There are several methods to produce synthetic filamented strands: dry spinning, gel spinning, melt spinning, phase-separation spinning, reaction spinning and wet spinning. Variations in the manufacturing process, such as heating/cooling differences and drawing differences, impart inconsistencies in the strand material that typically appear in widely varying inherent hot air shrinkage. Hot air shrinkage is the reduction in the dimensions of a fabric, yarn, or fiber induced by exposure to dry or wet heat and is a fundamental property of fibers. Once manufactured, these strands are used in the manufacture of yarns, for example sewing threads. The vagaries in the strands are further manifested during the manufacturing steps used to form the finished yarn product.
The following discrete process steps are typically employed during the manufacture of yarns to yield a final end product. First, there is the "spinning" step (to be distinguished from the spinning described above) where strands of cotton, wool and/or synthetic fiber is spun into yarn and wound onto small bobbins. These small bobbins are typically steam treated prior to further processing in a "twist setting" step. The yarn from these small bobbins are wound in serial fashion (i.e., the end of one bobbin is spliced onto the end of the next bobbin) to form larger bobbins or run-off spools of yarn. Several of these run-off spools are then placed on a creel and the yarn from each of the run-off spools are fed or delivered to a "doubling" or "plying" process. In the doubling process two or more yarns from the individual run-off spools are wound together to form a doubled yarn package. Typically, the doubled yarn packages are then used in a "twisting" operation as the final mechanical processing step prior to dyeing and finishing.
As mentioned, the variances in the manufacturing of the strands results in strand material having varying hot air shrinkage. When these strands are processed in the spinning and winding steps during yarn manufacture, and subjected to all the physical handling of the different yarn packages, all of which occurs prior to the strands being used in the doubling process, the resultant finished yarn packages are found to have highly undesirable vagaries. These vagaries ultimately manifest themselves as operational problems when the finished yarns are eventually employed in their designed end use, such as in sewing threads. For example, by the time the strands become part of a run-off spool they may have developed nonuniform and widely varying inherent hot air shrinkages or have hot air shrinkages much greater or less than other run-off spools of the same material. Given the fact that each run-off spool may contain strands having varying physical characteristics, the vagaries are further magnified when the strands from the multiple run-off spools are combined in the doubling process to form the plied yarn of the doubled package.
These compounded inconsistencies of the strands ultimately manifest themselves when the final yarn product is employed by the end user. For example, if the yarn being manufactured is a sewing thread, then the variances in the physical characteristics of the strands manifest themselves as inconsistency in the stitch balance. This is typically observed by the sewing machine operator as random loops on the underside of the sewn material. In attempting to correct stitch imbalance, the sewing machine operator will typically increase the tension on the sewing machine. This increased tension can result in skipped stitches and as the tension is further increased can eventually cause thread breakage. Skipped stitches and thread breakage are economically unacceptable to garment manufacturers. Unfortunately, the variances in the final yarn products, caused by the vagaries inherent in the stands, can only be detected when the yarn is put to its actual end use. Conventional physical examination of the plied yarn or the final yarn product does not typically reveal the inherent vagaries caused by the manufacturing of the strands and the manufacturing steps employing the strands to make finished yarns. The only accurate way to measure the vagaries is by statistically measuring the finished yarn under actual commercial use. For example, an electronic data collection system can be used to measure the number of work pieces sewn per stitch break.
Yarn manufacturers have recognized for some time the need to try and eliminate the obvious variances caused by the different processes and handling steps that occur during the manufacture of yarn For example, there is a number of patents directed to devices for spools of yarn obtained after the spinning. U.S. Pat. No. 4,523,441 (Braybrook et al.) teaches a method to reduce or regulate the quantity of fly or lint from production yarn by providing an apparatus that introduces humidity to a flow of air that impinges on textile yarn being wound or unwound. Another example are the methods and apparatuses for steam-setting bobbins of yarn produced by a spinning process as disclosed in U.S. Pat. No. 4,953,368 (Kawascki et al.) and U.S. Pat. No. 5,291,757 (Wanger). Likewise, the art has made attempts to improve the doubling process by including yarn guides or prestrengthening devices or detectors to determine when a yarn breaks. In U.S. Pat. No. 5,044,150 (Stahlecker) yarn detectors indicate broken yarn, stopping the process and activating an automatic piecing device to reconnect the yarn. U.S. Pat. No. 4,943,009 (Gerstner-Stevens et al.) discloses an improved plying process wherein a sensor is employed to detect the presence and absence of threads along a predetermined path. This sensor allows for automating the binding together of thread with a new spool when a given run-off spool becomes empty.
The combined teaching of the art, however, has not recognized that the variances in the physical properties of the strands themselves as a result of the manufacturing steps use to make the strands combined with the mechanical manipulations that occurs during yarn manufacture. The combined effect causes operational problems in the end use of the finished yarn product. Likewise, the art has not discovered that a high temperature thermal treatment of the strands prior to being plied in a doubling process, with controlled tensioning, results in a greatly improved doubled yarn and dramatically increased performance of the ultimate finished yarn product.